1. Field of the Invention
The present invention relates to a printing unit arrangement in a web-fed rotary printing press. In particular, the present invention relates to a printing unit arrangement in a lithographic web-fed rotary printing press which allows to print a 4/4 image on both sides of a paper web and which also allows for edition changes while the printing press is in operation.
2. State of the Art
In a lithographic web-fed rotary printing press, a running paper web is usually fed through a plurality of blanket-to-blanket printing units, which apply a multicolor image to both sides of the web. For driving the printing units, different drive systems, drive principles and configurations of drive motors and drive gears are known from the prior art.
One of the most common driving principles used in combination with blanket-to-blanket printing units uses one single drive motor per printing unit, in order to drive the couples of associated plate and blanket cylinders which are mechanically coupled via meshing drive gear wheels. Although this principle is the most cost effective principle, the coupling of the plate and blanket cylinders via meshing gear wheels does not allow for flying imprinter operations which are necessary for edition changes and changes of spot colors in the printed image, while the printing press is in operation. Accordingly, these printing units do not offer a high flexibility and also require a shutdown of the printing presses for a comparatively long time, in order to exchange printing plates and/or the printing units in case of an edition change.
U.S. Pat. No. 6,032,579 describes a blanket-to-blanket printing unit for a lithographic web-fed rotary newspaper printing press, in which the two blanket cylinders are mechanically coupled via drive gears which are driven by a first drive motor. Each of the two plate cylinders associated with one of the blanket cylinders is driven by its own independent drive motor, respectively. Due to the simultaneous control of the three independent drive motors, this highly flexible printing unit requires a sophisticated and therefore costly and complex control system.
EP 0 820 861 A2 purports to disclose a blanket-to-blanket printing unit, in which the two blanket cylinders and one of the plate cylinders can be mechanically coupled to each other to be driven by a first drive motor, whereas the second plate cylinder is separately driven by a second drive motor, in order to perform a flying imprinter operation on one side of the web. In order to perform a flying imprinter operation on the other side of the web, the drive gear wheel associated with the first drive motor can be brought out of mesh with the gear wheels of the blanket cylinders, and a further gear wheel coupled to the drive shaft of the second drive motor can be brought into mesh with the blanket cylinder drive gear wheels.
Due to the movable drive gear wheels, the print quality which can be obtained with the above-described printing unit is rather low compared to printing units, in which the drive gear wheels of the printing unit cylinders are in a constant mesh. Moreover, the document does not give any teaching to use the described 2-motor-drive printing unit in combination with other printing units in a tower arrangement.